1. Field of Invention
The present invention relates to a position sensor for oil-operated piston/cylinder units.
The invention relates, particularly but not exclusively, to a sensor adapted for installation in the cylinder and provided with a cursor, which cursor is mounted for displacement along a linear potentiometer and associated with one end of the piston to provide an indication of the piston travel.
2. Background Art
As is well known in this technical field, there are a large number of industrial applications where the position and/or the displacement of moving parts of power driven equipment must be reported.
Equipping oil-operated piston/cylinder units with position transducers in order to obtain an indication of the piston linear travel inside the cylinder is long-established practice.
In other words, the position transducers used in oil-operated piston/cylinder units are capable of detecting the piston travel with a relative precision.
Such position transducers are usually of the potentiometer type and comprise a sensor consisting of a linear potentiometer formed with conductive tracks, and a cursor associated with the piston head for displacement along the potentiometer.
Although on several counts advantageous and substantially successful, these prior transducers have some deficiencies, as specified here below.
First, the potentiometer conductive track is submerged in an oil bath inside the cylinder, which may impair the potentiometer reliability and precision in the event of even a small amount of water being present therein.
To obviate this problem, special oils are used that are guaranteed water-free, but that are also highly expensive.
Then, there are many applications where cylinders are operated in an unfriendly environment, e.g. under a low-temperature condition. In this case, the low temperature makes the working oil more viscous inside the cylinder, which may cause the cursor wipers to be pushed off the conductive tracks, albeit temporarily only, and result in faulty contacting.
Furthermore, the very high oil pressure inside the piston/cylinder unit makes its working conditions quite severe, resulting in premature sensor wear and deterioration.
In this context, taking down and replacing the sensor for maintenance or servicing may pose problems. In many cases, replacing the sensor may take several hours of skilled work, with attendant general difficulties and economic losses from downtime.
The state of the art provides no improvements to position sensors installed inside piston/cylinder units as can obviate the above deficiencies.
A magnetic coupling type of position sensor is disclosed in PCT Patent No. WO 98/17974 to Data Instruments, Inc.
However, that sensor is intended for use as a level sensor, and no mention is made in the patent specification of a possible use of the sensor inside piston/cylinder units, nor are the problems that this involves addressed thereby.
The aim of the present invention is that of providing a linear position transducer, or linear position sensor, with suitable constructional and functional features for use inside oil-operated piston/cylinder units and operation under a very high working pressure, such that it can overcome the deficiencies of the prior sensors discussed hereinabove.
A further object of the invention is that of providing a oil-operated piston/cylinder unit including a position sensor having an improved structure to allow operation under very high pressure.
The principle on which this invention stands is that of housing the sensor a sealed and armored case to be included in the cylinder; a magnetic coupling is established between a sliding magnetic actuator placed outside the case and a cursor inside the sensore.
In this way, the sensor is substantially enclosed and fully protected against the unfriendly environment in which it is expected to operate.
The invention provides a position sensor installed inside a cylinder of a oil-operated piston/cylinder units, comprising:
a linear potentiometer being associated with one piston end to provide an indication of the piston travel;
a cursor mounted for displacement inside said linear potentiometer; said potentiometer and said cursor being housed within an armored case;
a magnetic actuator associated with the piston and slidable along the outer surface of said case in magnetic coupling relationship with said cursor.
The invention further provides a oil-operated piston/cylinder unit including a position sensor installed inside a cylinder of the piston/cylinder unit and comprising:
an armored case;
a linear potentiometer of a position transducer being house in said armored case and associated to one end of said unit for providing an indication of the piston travel;
a cursor mounted for displacement inside said linear potentiometer;
a magnetic actuator associated with the piston and slidable along the outer surface of said armored case in magnetic coupling relationship with said cursor.
The features and advantages of a position sensor according to the invention will be apparent from the following description of an embodiment thereof, given by way of non-limiting example with reference to the accompanying drawings.